A betting bankroll calculator turns a pot of money into a staking plan. Start with $1,000 and bet 2% a time and your unit is $20. Win 53% of your bets at -110 over a 500-bet season and you’d expect to finish about $118 up. Sounds modest. Then look at the swings: one standard deviation over the season is about $425, and you should expect at least one run of six straight losers. The free calculator above puts all of that on one screen.
Betting unit calculator: how your unit is set
A unit is a fixed slice of your bankroll, the stake for a normal bet. Most bettors who last use 1% to 3%. At 1% you can absorb almost anything. At 5% a bad week does real damage. Above that, a long losing run (and it will come) can take most of the bankroll.
Unit = bankroll × unit % Longest losing run ≈ ln(n × p × (1 − p)) ÷ ln(1 ÷ (1 − p))
Recalculate the unit when the bankroll moves by a quarter or so, up or down. That’s a simple way to stake proportionally without fiddling with every bet.
Reading the numbers
The break-even rate is the first thing to check. At -110 you need 52.38% just to stand still. The expected profit only becomes positive above that, and the risk of ruin is only meaningful if you’re above it too: below break-even, the bankroll shrinks however you stake it.
The losing-run figure is an estimate of the longest streak you should expect, not the worst possible. Over a few seasons, longer runs turn up. The losing streak calculator shows the odds for any run length.
If you have a reliable edge per bet, the Kelly criterion calculator gives a stake that grows the bankroll fastest, and the risk of ruin calculator goes deeper on the chance of going broke.
Before sizing stakes, check your strike rate against the odds you back with the win percentage calculator.
Bet with money you can afford to lose. If it stops being fun, BeGambleAware.org is free and confidential.